Typical gas turbine engine fuel supply systems include a fuel source, such as a fuel tank, and one or more pumps that draw fuel from the tank and deliver pressurized fuel to the fuel manifolds in the engine combustor via a main supply line. The main supply line may include one or more valves in flow series between the pumps and the fuel manifolds. These valves generally include at least a main metering valve and a pressurizing-and-shutoff valve downstream of the main metering valve. In addition to the main supply line, many fuel supply systems also include a bypass flow line connected upstream of the metering valve that bypasses a portion of the fuel flowing in the main supply line back to the inlet of the one or more pumps, via a bypass valve. The position of the bypass valve is typically controlled by a head regulation scheme to maintain a substantially fixed differential pressure across the main metering valve.
The above-described fuel supply system, in many instances, uses a proportional head regulation control scheme. While generally safe, reliable, and robust, a proportional control scheme can suffer certain drawbacks. In particular, it can result in an error (or “droop”) of the controlled pressure drop, which may be relatively significant. For example, the error can be up to about 4% in some systems. To substantially eliminate this proportional droop error, some systems have implemented a proportional plus integral control scheme. While this alternative works generally well, and is also generally safe, reliable, and robust, it also suffers certain drawbacks. For example, it can result in increased system complexity and cost.
Hence, there is a need for a system and method of providing compensating for proportional pressure droop error in fuel flow control systems that does not result in increased system complexity and/or system cost. The present invention addresses one or more of these needs.